Monitor systems are proposed for internal pressure of tires provided in a vehicle. One monitor system includes a sensor unit disposed in each tire and a monitor unit disposed in a vehicle body. The sensor unit has a sensor for detecting internal pressure of each tire and a transmitter for sending the detected internal pressure. The monitor unit receives the detected internal pressure from the transmitter of the sensor unit to give warning when the detected internal pressure is smaller than a predetermined value.
Here, a unique identification code (ID code) is assigned to the sensor unit and registered in the monitor unit. The unique ID code accompanies the detected internal pressure that is sent to the monitor unit, so that the monitor unit can determine whether the received internal pressure is sent from its own sensor unit. When the ID code of the sensor unit is successfully verified, the monitor unit then determines whether the received internal pressure is adequate. Using the ID code assigned to each sensor unit gives reliability to the monitor system.
Here, the ID code of the sensor unit provided in each tire is registered to the monitor unit as follows. Through a predetermined switching manipulation the monitor unit is shifted from a monitoring mode (normal mode) to a registering mode. For instance, decompressing an internal pressure of a tire forcibly causes a corresponding sensor unit to send a signal with the ID code. When the monitor unit is in the registering mode, the received ID code of the sensor unit is registered in the monitor unit.
However, in a conventional tire pressure monitor system, switching into the registering mode or completion of registering the ID code is shown in a display such as an LED (light emitting diode) that is located inside a cabin of the vehicle. When an operator registering the ID code forcibly sends the ID code from the sensor unit of the tire, he must confirm, through observing the display inside the cabin of the vehicle, whether the ID code is surely registered in the monitor unit. Necessity of repeatedly observing the display inside the cabin decreases operation efficiency in registering the ID code.